Film winding core, and wound film body using same

ABSTRACT

A film winding core ( 10 ) of the present invention includes a core body ( 12 ) and a plurality of film supporting portions ( 14 ). The core body ( 12 ) has a tubular shape. The plurality of film supporting portions ( 14 ) are provided around the core body ( 12 ). The film supporting portions ( 14 ) protrude from the outer peripheral surface ( 12   p ) of the core body ( 12 ) respectively at a plurality of positions in a rotational direction of the core body ( 12 ) so that a film ( 18 ) is supported away from the outer peripheral surface ( 12   p ) of the core body ( 12 ). Each of the film supporting portions ( 14 ) is made of a material that can be deformed when the film ( 18 ) is wound on the film winding core ( 10 ).

TECHNICAL FIELD

The present invention relates to a film winding core and a wound filmbody using the core.

BACKGROUND ART

A long film is produced by a known method such as extrusion molding andwound on a cylindrical core for storage and shipment. The film thuswound on the cylindrical core is distorted (deformed) during storage,which may cause difficulties in unwinding the film. For example, PatentLiterature 1 points out such a problem.

Patent Literature 1 describes a core configured to prevent thedistortion of a belt-like article resulting from the contraction of thewound article. Specifically, after the belt-like article is wound on thecore in close contact with the outer periphery of the core, the core iscontracted in the radial direction thereof. Then, after the core isexpanded in the radial direction to increase the contact between theouter periphery of the core and the belt-like article, the belt-likearticle is unwound from the core.

CITATION LIST Patent Literature

Patent Literature 1: JP 2009-113877 A (FIG. 5 to FIG. 10)

SUMMARY OF INVENTION Technical Problem

Since the core described in Patent Literature 1 has a relatively complexmechanism, it is not suitable for sale to customers in the form of aroll of film wound on the core.

It is an object of the present invention to provide a simple techniquefor preventing defects in unwinding the film.

Solution to Problem

The present invention provides a film winding core on which a long filmis to be wound. This film winding core includes: a core body having atubular shape; and a plurality of film supporting portions providedaround the core body. The film supporting portions protrude from anouter peripheral surface of the core body respectively at a plurality ofpositions in a rotational direction of the core body so that the film issupported away from the outer peripheral surface of the core body, andeach of the film supporting portions is made of a material that can bedeformed when the film is wound on the film winding core.

In another aspect, the present invention provides a wound film bodyincluding: the film winding core of the present invention; and a filmwound on the film winding core of the present invention.

Advantageous Effects of Invention

To the inventors' knowledge, a film is distorted based on the followingmechanism. Depending on the production method of the film, a long filmhas not a little thickness unevenness (variations in the thickness) in awidth direction. When such a film is wound on a conventional cylindricalcore, a thick portion of the film expands outward more than a thinportion thereof. Then, tension is concentrated on the thick portion, andthe thick portion is stretched in the longitudinal direction. On theother hand, sufficient tension is not applied to the thin portion, andso-called “gapping” occurs in some cases. “Gapping” refers to theformation of a gap between the inner layer and the outer layer of thewound film. In the case where the film is wound on the core and then thewound film is stored in a temperature environment in which the filmcontracts, a gapped portion of the film contracts in the longitudinaldirection to eliminate the gap. As a result, distortion between thethick portion and the thin portion increases. This makes a difference inthe longitudinal length between the thick portion and the thin portion.

This distortion is memorized in the film. Therefore, the film is unwoundfrom the core while keeping the distortion. Then, sufficient tension isnot applied to the thick portion, which causes a slack in the thickportion. This phenomenon is most obvious when the tension applied to thefilm is not high enough to unwind the film. The slack in the film causeserrors in feeding the film, and reduces the yield of film-relatedproducts and the availability of the film.

According to the present invention, the plurality of film supportingportions are provided around the core body. Since the film supportingportions protrude from the outer peripheral surface of the core body,the film is supported by the film supporting portions. Therefore, it ispossible to prevent the film from coming into close contact with thecore body between two film supporting portions that are adjacent to eachother in the rotational direction. Thus, it is possible to prevent asmuch as possible the distortion from being memorized in the film. Inaddition, the film supporting portions are made of a material that canbe deformed when the film is wound. The deformation of the filmsupporting portions can alleviate or offset the influence of the uneventhickness of the film.

As described above, according to the core of the present invention, thedistortion caused by the uneven thickness can be suppressed. Therefore,the bend or slack in the film can be prevented during unwinding of thefilm. As a result, stable feeding of the film can be achieved duringunwinding thereof, and thus the incidence of manufacturing defects(feeding errors) can be reduced significantly. The yield of film-relatedproducts and the availability of the film are also improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a film winding core according to anembodiment of the present invention.

FIG. 2 is a cross-sectional view of the core shown in FIG. 1, takenalong the line II-II.

FIG. 3 is a cross-sectional view of a wound film body using the coreshown in FIG. 1.

FIG. 4 is a schematic view showing a preferable protrusion height offilm supporting portions.

FIG. 5A is a cross-sectional view of a core according to a modification.

FIG. 5B is a cross-sectional view of a core according to anothermodification.

FIG. 5C is a cross-sectional view of a core according to still anothermodification.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the accompanying drawings. Hereinafter, in thisdescription, the film winding core is simply referred to as a “core”.

As shown in FIG. 1 and FIG. 2, a core 10 is composed of a core body 12,a pair of bearing portions 16, and a plurality of film supportingportions 14. As shown in FIG. 3, a wound film body 100 includes the core10 and a long film 18 wound on the core 10. The core 10 can be rotatedabout a rotational axis O. The rotational axis O is an axis passingthrough the center of the core body 12.

The core body 12 has a tubular shape. For example, the core body 12 canbe formed of a tubular member with both ends open. The cross-sectionalshape of the core body 12 is not particularly limited. The shape may bea circle as in the present embodiment, or it may be a polygon. In thiscore 10, the film 18 is supported directly by the film supportingportions 14. Furthermore, as described later, the influence of theuneven thickness of the film 18 is cancelled out by the film supportingportions 14. Therefore, a high dimensional accuracy is not required forthe core body 12.

The material of the core body 12 is not particularly limited. The corebody 12 can be made of resin, metal, ceramic, glass, or a combination ofthese. Desirably, the core body 12 is not easily deformed when the film18 is wound on the core 10. Typically, the core body 12 can be obtainedby molding a thermoplastic resin, such as polycarbonate, polypropylene,polyethylene, acrylonitrile-butadiene-styrene copolymer, polyester (forexample, polyethylene terephthalate, polyethylene naphthalate or thelike), polystyrene, or polyvinyl chloride, by a known method, forexample, by injection molding.

The film supporting portions 14 are portions provided around the corebody 12, and protrude radially outwardly from the outer peripheralsurface 12 p of the core body 12 respectively at a plurality ofpositions in the rotational direction of the core body 12 so that thefilm 18 is supported away from the outer peripheral surface 12 p of thecore body 12. According to the film supporting portions 14, the closecontact between the film 18 and the core body 12 can be avoided betweenthe film supporting portions 14 that are adjacent to each other in therotational direction. Thus, it is possible to prevent the distortionfrom being memorized in the film 18.

The film supporting portions 14 are made of a material that can bedeformed when the film 18 is wound on the core 10. In the presentembodiment, the film supporting portions 14 are made of an elasticallydeformable material. When the film supporting portions 14 areelastically deformable, sufficient friction can be generated between thefilm supporting portions 14 and the film 18. Therefore, free rotation ofthe core 10 can be prevented when the film 18 is wound and unwound. Inaddition, since the film supporting portions 14 have appropriate elasticand cushioning properties, the influence of the uneven thickness of thefilm 18 can be alleviated or offset effectively.

Typically, at least one material selected from the group consisting ofsponge, rubber, and foam can be used as a material for the filmsupporting portions 14. These materials are all inexpensively availableand easy to process. These materials also allow sufficient friction toact between the film 18 and the film supporting portions 14. Forexample, since urethane foam has the above-mentioned properties in awell-balanced manner, it is recommended as the material for the filmsupporting portions 14. Materials having appropriate impact resilienceare, for example, natural rubber, nitrile rubber, silicone rubber, andfoams of these. Besides these materials, polyethylene, EVA(ethylene-vinylacetate copolymer), EPDM (ethylene-propylene-dienerubber), fluorine rubber, and foams of these also can be used. The filmsupporting portions 14 can be fixed to the core body 12 by a knownmethod such as bonding or welding.

The entire film supporting portion 14 does not have to be made of anyone of the above materials. Only a portion of the film supportingportion 14, for example, a portion in contact with the film 18 may bemade of any one of the above materials.

In the present embodiment, the film supporting portions 14 are arrangedat regular intervals (regular angular intervals) in the rotationaldirection of the core body 12. The film supporting portions 14 arrangedat regular intervals in the rotational direction improves the uniformityof load on the film 18 in the longitudinal direction of the film 18.This has an advantage in suppressing the distortion.

As shown by a dashed line in FIG. 4, an imaginary polygon PL having aminimum area required to surround all the film supporting portions 14 ina cross-section perpendicular to the rotational axis O is defined. Thepositions of the film supporting portions 14, the number of the filmsupporting portions 14, the height h of the film supporting portions 14protruding from the outer peripheral surface 12 p of the core body 12can be adjusted so that the core body 12 fits within this polygon PL.When these requirements are satisfied, the film 18 can be prevented frombeing strongly pressed against the core body 12. For example, a core 10Ashown in FIG. 5A has the film supporting portions 14 provided at regularintervals at eight positions thereon in the rotational direction.

The film supporting portions 14 are provided so as to extend from oneside of the core body 12 to the other side thereof. The longitudinaldirection of the film supporting portion 14 is parallel to therotational axis O of the core 10, and is perpendicular to thelongitudinal direction of the film 18. This configuration allows auniform supporting force to be applied to the film 18 in the widthdirection of the film 18.

In the present embodiment, the film supporting portion 14 has asemicircular column shape. This shape allows the film supporting portion14 to have a reasonably large surface area for supporting the film 18.This is preferred from the viewpoint of preventing a local deformationof the film 18. A core 10B shown in FIG. 5B is provided with filmsupporting portions 24 having a hollow semicircular column shape. A core10C shown in FIG. 5C is provided with film supporting portions 34 havinga rectangular column shape. These film supporting portions 24 and 34also can be suitably employed because they perform the same action asthe film supporting portions 14. In particular, since the filmsupporting portions 24 having a hollow structure as shown in FIG. 5B canbe easily elastically deformed, the effect of alleviating or offsettingthe influence of the uneven thickness of the film 18 can be expectedsufficiently. In the cross-section perpendicular to the rotational axisO, the outer peripheral surface of the film supporting portion 14 or 24has a smaller curvature than that of the outer peripheral surface 12 pof the core body 12.

The bearing portions 16 are portions which are mounted on both sides ofthe core body 12 and into which a shaft (not shown) used to rotate thecore 10 is to be inserted. The core 10 can be rotated smoothly by thebearing portions 16. The bearing portions 16 have the same contour asthe core body 12. However, the bearing portions 16 have a largerdiameter than that of the core body 12, which means that the bearingportions 16 may extend beyond the core body 12.

In the present embodiment, the bearing portions 16 are each constitutedby a disc-shaped flange having a bearing hole 16 h. The bearing portions16 may be integrated with the core body 12, or may be detachable fromthe core body 12. In the former case, the bearing portions 16 can beintegrated with the core body 12 by a known method such as welding orbonding. In the latter case, fitting structures can be provided betweenthe core body 12 and the bearing portions 16. In the case where thebearing portions 16 are detachable, this one pair of bearing portions 16can be shared by many cores 10. Therefore, the cost of the core 10 canbe reduced. In addition, since the weight of the wound film body 100 canbe reduced by removing the bearing portions 16 therefrom, a reduction inthe transportation cost for delivery to a customer also can be expected.The bearing portions 16 are not essential components, of course. Theshaft can be inserted directly into the core body 12 so as to rotate thecore 10.

As used in this description, the “bearing portion 16” may not have afunction of supporting the shaft, to be exact. The term “bearingportion” is used in the sense of “a portion having a through-hole(bearing hole 16 h) for mounting the core 10 on the shaft”.

Since the core 10 of the present embodiment does not have a mechanicallymovable portion, it can be produced at low cost.

As shown in FIG. 3, the wound film body 100 has a polygonal shape,typically a regular polygonal shape, as a whole, in the cross-sectionperpendicular to the rotational axis O (or in plan view). In the woundfilm body 100, gaps SH are formed between the outer peripheral surface12 p of the core body 12 and the film 18. Portions of the film 18 woundon the core 10 that are not supported by the film supporting portions 14are slightly slackened toward the core body 12. In this state, the film18 may be completely separated from the core body 12 or may be incontact with the outer peripheral surface 12 p unless the effect ofsuppressing the distortion decreases significantly.

The material, structure and dimensions of the film 18 to be wound on thecore 10 are not particularly limited. However, the use of the core 10 ofthe present embodiment for winding a film having thickness unevennessinherent thereto is very effective in suppressing the distortion. Forexample, a film produced using an extruder equipped with a T-die has anapproximately uniform width-direction thickness distribution in anyportion of the film measured in the longitudinal direction. For example,it is assumed that there is a thickness difference of about 1 μm betweenone end of the film and the other end thereof in the width direction.When this film is wound 1000 turns on a conventional cylindrical core, adiameter difference of about 2 mm is created between one end of theresulting wound film body and the other end thereof. Even such slightthickness unevenness increases the diameter difference in the resultingwound film body as the number of winding turns increases. As a result,the distortion due to the uneven thickness is memorized in the film,which increases the probability of unwinding defects (typically feedingerrors).

The core 10 of the present embodiment is particularly effective inwinding a film which is hard to remove distortion once the distortion ismemorized in the film. Such a film has flexibility, and typically it hasa thickness of micrometer order (for example, 2 to 100 μm).

Generally, there are few cases where the film having an uneven thicknessitself has a great influence on the quality of a final product, forexample, a secondary battery. As described above, even if a film hasthickness variations of about ±1 μm from a target thickness of 20 μm,such variations in the thickness of the film are unlikely to have aninfluence on the quality of the final product as long as the otherproperties of the film meet the standards. Indeed, if the film has acompletely uniform thickness, it is expected that unwinding defectscaused by thickness unevenness rarely occur. However, it is verydifficult and impractical to reduce the variations of ±1 μm to ±0.1 μmby improving the production method of the film. According to the presentinvention, it is possible to prevent defects caused by the uneventhickness of the film by improving the core, instead of improving thefilm itself.

The film produced using an extruder equipped with a T-die is, forexample, a porous resin membrane. Examples of the porous resin membraneinclude porous membranes made of polyolefin, fluorine resin,polyurethane, polyamide, polyester, polyimide, polyamide-imide, epoxy,and the like. Examples of polyolefin include polyethylene andpolypropylene. Examples of fluorine resin includepolytetrafluoroethylene. A porous resin membrane made of polyimide,polyamide-imide or epoxy may be a thermosetting membrane. These porousresin membranes can be widely used for applications such as a separatorfor an electrochemical device, a waterproof gas permeable membrane, adust collecting filter, and a low dielectric substrate.

The film 18 may or may not have an adhesive layer. However, a filmhaving no adhesive layer is more suitable for use with the core 10 ofthe present embodiment. Generally, once a film having an adhesive layeradheres to something, a high tension is required to remove the film.Therefore, even if the film is slightly distorted, such distortion isunlikely to cause feeding errors. In contrast, a film having no adhesivelayer, more specifically, a film having slidable front and backsurfaces, is often unwound at a low tension and a high speed for use.The higher the unwinding speed, the higher the probability of a feedingerror. Therefore, it is particularly recommended to use the core 10 ofthe present embodiment as a core for a film having no adhesive layer.

1. A film winding core on which a long film is to be wound, comprising:a core body having a tubular shape; and a plurality of film supportingportions provided around the core body, the film supporting portionsprotruding from an outer peripheral surface of the core bodyrespectively at a plurality of positions in a rotational direction ofthe core body so that the film is supported away from the outerperipheral surface of the core body, and each of the film supportingportions being made of a material that can be deformed when the film iswound on the film winding core.
 2. The film winding core according toclaim 1, wherein the material is an elastically deformable material. 3.The film winding core according to claim 1, wherein the materialcomprises at least one selected from the group consisting of sponge,rubber, and foam.
 4. The film winding core according to claim 1, whereinthe film supporting portions are arranged at regular intervals in therotational direction.
 5. The film winding core according to claim 1,wherein the positions of the film supporting portions, the number of thefilm supporting portions, and a height of the film supporting portionsprotruding from the outer peripheral surface of the core body areadjusted so that the core body fits within a polygon having a minimumarea required to surround all the film supporting portions in across-section perpendicular to a rotational axis of the film windingcore.
 6. The film winding core according to claim 1, wherein the filmsupporting portions are each provided so as to extend from one side ofthe core body to the other side of the core body, and a longitudinaldirection of the film supporting portion is parallel to a rotationalaxis of the film winding core.
 7. The film winding core according toclaim 1, wherein the film supporting portion has a shape of asemicircular column, a rectangular column, or a hollow semicircularcolumn.
 8. The film winding core according to claim 1, furthercomprising a pair of bearing portions which are mounted on both sides ofthe core body and into which a shaft used to rotate the film windingcore is to be inserted.
 9. The film winding core according to claim 8,wherein the bearing portions are constituted by a pair of flanges eachhaving a bearing hole and being detachable from the core body.
 10. Awound film body comprising: the film winding core according to claim 1;and a long film wound on the film winding core.
 11. The wound film bodyaccording to claim 10, wherein the film is a film produced using anextruder equipped with a T-die.
 12. The wound film body according toclaim 11, wherein the film is a porous resin membrane.